1. Field of the Invention
The invention relates to an apparatus and a method for the treatment of workpieces with fluids in general and for the coating of hollow bodies in particular.
2. Background of the Invention
Plastics, in particular transparent plastics, are becoming increasingly important and in many sectors are displacing glass as the preferred material.
One example includes drinks bottles, which a few years ago were made almost exclusively from glass but nowadays are already to a large extent being made from PET. The reason for this is the huge weight saving.
However, plastic bottles may also have a number of drawbacks compared to glass bottles, for example the plastics used, such as PET, are insufficiently impervious to gases, and consequently the shelf life is shorter, in particular in the case of carbonated drinks, than with glass bottles unless special measures are implemented.
For this reason, plastic bottles are internally provided with a coating, which leads to an increase in the shelf life.
Since drinks bottles are mass-produced products, there is a huge pressure on cost, and consequently there is an ongoing demand for improvements to the coating methods and the apparatuses used for them.
Accordingly, to efficiently coat PET bottles and other workpieces made from dielectric material, preferably plastics, it is desirable to develop an apparatus and a method which allow very short cycle times and therefore a high throughput. Typical throughputs required are in the region of 10000 bottles per hour.
WO00/58631 has disclosed a machine of this type with a conveyor carousel for the treatment of hollow bodies, in which 20 identical treatment stations are arranged on the conveyor carousel.
The invention defined in the document referred to above is based on the problem that with a large number of treatment stations there is a risk of two adjacent treatment stations being simultaneously connected to the same pressure source.
In the above document, the proposed solution is to provide a machine having a first pumping phase and a second pumping phase as well as a deposition phase in which the stations for the various phases are connected to pumps. Furthermore, it is assumed that the weight and volume of the pumps prevent them from being mounted on the carousel. Therefore, the pumps are in a fixed position and a rotating connection or distributor is used to connect the pumps to the stations.
Furthermore, the 20 stations are divided into two groups, each group being assigned to an independent and equivalent pressure source, or the groups being differentiated on the basis of which pumps they are connected to. The rotating distributor determines the instants during the rotary movement of the conveyor carousel at which a certain pump is connected to a certain treatment station, the distributor for this purpose having a rotating ring comprising 20 openings and a fixed ring comprising in each case 3 slots for the two groups. To benefit from this arrangement, the machine is designed in such a way that two stations of the same group are not simultaneously connected to the corresponding pump.
Accordingly, the invention described defines as its subject matter a machine which is able to include a large number of stations and at the same time to ensure that a pressure source at a defined instant is only connected to at most one treatment station.
However, this machine has a number of serious drawbacks.
Firstly, the parallel connection of a plurality of pumps is disadvantageous, since multiple tube routing is required.
Furthermore, the stationary arrangement of the pumps is disadvantageous, since the paths from the stations to the pump are relatively long and therefore the pump power is reduced.
However, the use of the rotatable distributor is particularly disadvantageous. Distributors of this type are extremely difficult to seal and are susceptible to faults caused by foreign bodies. Furthermore, on account of the fixedly predetermined opening arrangement, the distributor does not allow any variation to the process sequence and therefore this represents an inflexible design.
However, it is not only the method which takes place on the abovementioned apparatus but also the coating of amorphous carbon used which is in need of improvement, since this coating is undesirably colored. Furthermore, there is a risk of the layer of carbon flaking off in the event of deformation to the bottle.